Arrangement for magnetic beam concentration



y 1958 w. KLEIN ETAL 2,843,789

ARRANGEMENT FOR MAGNETIC BEAM CONCENTRATION Filed July e, 1953 ATTORNEY United States Patent ARRANGEMENT FOR MAGNETIC BEAM CONCENTRATION Werner Klein, Korntal, and Walter Friz, Stuttgart, Germany, assignors to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application July 6, 1953, Serial No. 366,288

Claims priority, application Germany July 5, 1952 1 Claim. (Cl. 315-35) This invention relates to a magnetic beam focusing arrangement particularly for use in traveling wave tubes.

Magnetic fields have been widely used in traveling wave tubes for concentrating the electron beam. The magnetic field is generated by a coil surrounding the beam along its entire path, but in the case of traveling wave tubes, the coil must be interrupted to allow for wave input and output coupling means, and in most cases the coil consists of three separate portions. In the spaces be tween the three coil portions, the field is no longer uniform. In known structures the deviations of the magnetic field and the non-uniformity of the field was decreased by making coils whose inner radius was large in comparison with the beam diameter. This required use of large coils with their attendant high direct current losses and heavy copper weights. The object of the present invention is the provision of improved means for diminishing the disturbances in magnetic fields which are intended to be uniform and have one direction of flux.

In accordance with a feature of the present invention it is proposed that a sheath or cylindrical mantle of paramagnetic or ferromagnetic material of low permeability be arranged between the magnetic coil or parts of the magnetic coil and the electron beam. The thickness of the mantle of course depends on the desired permeability and the material used. The magnetic coil, in correspondence to its decreased inner diameter, will become smaller, and although the intensity of the internal flux field will be somewhat diminished by the mantle, this is easily overcome by a slight increase of total flux flow in order to obtain the required field intensity. By this arrangement the magnetizing power required will be considerably reduced as compared with the known arrangements. Dimensions and weight of the magnetic coil will likewise be reduced. By appropriate selection of the thickness of the cylindrical mantle and its permeability, the magnetic field will remain uniform in the region of the electron beam even in the spaces between the coils and between the portions of the cylindrical mantle. Furthermore the effect of minor irregularities in the winding of the coils will be overcome by the cylindrical mantles.

In accordance with a further aspect of the present invention, the cylindrical mantle is made of a material that has good attenuation for the highest frequencies, for example of a ferromagnetic substance like carbonyl iron. This may be in compressed powder form. This cylindrical mantle then serves to increase the attenuation of the wave travelling along the travelling wave tube transmission line, which may be for example, a helix. Naturally the cylindrical mantle can also be made of iron or nickel or any other ferromagnetic or paramagnetic materials. Since the cylindrical mantle lies between the helix and the magnetic coil, optimum attenuation will be obtained by an appropriate selection of the distance be tween the helix, the envelope of the travelling wave tube and the cylindrical mantle. This attenuation varies with frequency and increases with decreasing frequency since for lower frequencies the electromagnetic field around the helix will extend in greater measure into the surrounding space. This acts to suppress the tendency of the travelling wave tubes to oscillate at lower frequencies.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself Will be best understood, by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, in which there is disclosed a schematic diagram of a traveling wave tube.

Referring now to the drawing, a traveling wave tube 1 has an electron beam path 2 surrounded by a helix 3 with input and output coupling means 4 and 5. The beam is concentrated by magnetic coil portions 6 which closely surround the cylindrical mantle portions '7, the latter lying directly against the glass bulb of the tube. In one embodiment of the foregoing invention it was possible to obtain a reduction from 30 kg. to 8 kg. in the: weight of the copper wire with equal uniformity of the beam.

While we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of our invention as set forth in the objects thereof and in the accompanying claim.

What is claimed is:

A traveling wave tube amplifier comprising means for producing an electron beam, transmission means for propagating an electromagnetic wave parallel to and adjacent said beam, an enclosing envelope for said transmission means and said wave propagating means, input and output couplers at the ends of said transmission means, and means for concentrating said beam and for attenuating unwanted high frequency components produced in operation of said tube, comprising a sheath of paramagnetic material having a high attenuation factor for said unwanted high frequency waves, external of said envelope but closely adjacent thereto, and a magnetic beam concentrating coil surrounding said sheath substantially throughout the length of said tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,259,531 Miller et a1 Oct. 21, 1941 2,602,148 Pierce July 1, 1952 2,679,019 Lindenblad May 18, 1954 

